The seal between the bottom of the water compartment and the tubes in heat exchangers poses particular difficulties, especially in so-caled "seamless" heat exchangers, in which the tubes are not soldered to the water compartment while thin bottoms and thin tubes are used.
It is known to expand the tubes conically by appropriate presses following assembly with the water compartment bottom, in order thereby to produce a firm seat in the water compartment bottom. It is also known to provide the water compartment bottom in the immediate vicinity of each tube with an annular flange, a so-called "passage", which surrounds the tube for a specific portion of its length. In known heat exchangers of this type, sealing elements are provided between the passage and tube.